In general, the present invention relates to the removal of contaminants from mother liquors. More specifically, it relates to the removal of chloride and carbonate contaminants from mother liquors in a zeolite process.
Zeolites can be produced by forming sodium aluminate and sodium silicate solutions, adding together the two solutions to produce a reaction mixture comprising a mother liquor and an amorphous sodium aluminosilicate, reacting the reaction mixture to form a zeolite composition, recovering the zeolite composition from the reaction mixture, and recycling the mother liquor to the reaction mixture.
Before the mother liquor can be recycled, it must be treated to remove halide impurities, organic discoloring complexes, and ferruginous sludge. These impurities need to be removed because the commercial grade raw materials are typically produced in processes which give rise to halide (usually chloride) and carbonate contamination of the raw materials. Unless these impurities are removed, they will accumulate in the recycle stream and reach levels where they cause undesired reactions to occur.
These impurities can be removed by membrane-type cells, fractional crystallization, or similar units. They can also be removed by drawing off some of the recycle stream to a waste dump, but this wastes useful process liquids.
In U.S. patent application Ser. No. 168,833 filed July 10, 1980 by Claude Andrews, now U.S. Pat. No. 4,289,629, chloride and carbonate ion concentrations of a strongly alkaline solution can be reduced by the process of mixing sodium aluminosilicate into the solution, heating the resulting solution to a temperature of at least 90 degrees Celsius to form a sodalite type product, and filtering the sodalite type product from the solution.